1. Field of the Invention
The present invention relates to image reader apparatuses such as scanners used for digital copy machines and cylinder shaped lamps used for them.
2. Description of the Related Art
Conventionally, as shown in FIG. 1, in an image reader apparatus, a manuscript surface 3 of a manuscript 2 which is set on a manuscript stand 1 (a contact glass) is lighted by a cylinder shaped lamp 4 so as to form a line. A reflection light from a reading part 3A forming a line of the manuscript surface 3 lighted so as to form a line is image-formed to an imaging element 6 by an image-formation lens 5 which forms one part of a contraction optical system (an image-formation optical system), so that an image of the manuscript 2 is read.
A Xenon pipe is used as the cylinder shaped lamp 4, for example. An irradiation opening part 4A is provided at the Xenon pipe. The reading part 3A of the manuscript surface 3 is directly lighted by a lighting light P1 outgoing through an irradiation opening part 4A and lighted by a reflection lighting light P1′ reflected by a reflector 7.
The refection light from the reading part 3A is led to the contraction optical system by a turning mirror 8, so that the reflection light is image-formed to the imaging element 6 by the image-forming lens 5. The cylinder shaped lamp 4 and the reflector 7 move while scanning in a direction (a sub scanning direction) perpendicular to a direction (a main scanning direction) extending so as to make a line of the reading part 3A, so that image reading is implemented by a line sequence.
In reading of the manuscript image by the scanner, a quality of image reading is determined by photographic sensitivity of the imaging element 6 such as a charge coupled device (CCD), an optical performance of the contraction optical system such as the lens, a reading position, an emission amount of the cylinder shaped lamp 4, a light amount of a synthetic lighting light including the cylinder shaped lamp 4 and the manuscript surface 3. In a case where a distance from a lighting optical system including the cylinder shaped lamp 4 and the reflector 7 to the manuscript surface 3 is short, the lighting light which is diffused reflection at the manuscript surface 3 irradiates the reflector 7, the cylinder shaped lamp 4, and other optical parts provided inside of the housing of the image reader apparatus. As a result of this, the above-mentioned lighting light becomes a secondary lighting light which irradiates again to the reading part 3A of the manuscript surface 3, so that a flare phenomenon based on the change of the reading image signal is generated.
Accordingly, in the image reader apparatus, in order to prevent the generation of the flare due to exposure of the reading part 3A of the manuscript surface 3, it is necessary to prevent excess light other than the lighting light for exposure from being incident on the reading part 3A of the manuscript surface 3. Because of this, a structure providing glare protection is known conventionally. Furthermore, while a distance from the cylinder shaped lamp 4 to the manuscript surface 3 is long, a light collector lens is provided so as to prevent reduction of the amount of lighting light at the reading part 3A due to the long distance. A transparent opening part and a glare protection part are formed at the light collector lens, so that the reading part 3A can be lighted in a concentrated manner. As a result of this the flare is prevented from being generated. See Japan laid-open patent application H09-130540.
In another conventional art device, a lighting unevenness due to the reflection light is prevented from being generated by regarding a property of the exposure light amount in a direction where the line of the reading part 3A extends as a specific condition. See Japan laid-open patent application 2001-222076.
That is, as shown in FIG. 1, a part P2′ of the lighting light P1 which is diffused at the reading part 3A returns inside of the Xenon pipe through the irradiation opening part 4A and reflects at an inside wall surface 4B, so as to become a secondary lighting light P3′ which secondarily lights again the reading part 3A through the irradiation opening part 4A. Based on the secondary lighting light P3′, a flare phenomenon is generated.
Once the flare phenomenon is generated, even if there is the reading part 3A having the same manuscript density, the reading image signal by the scanner is changed due to the density difference in the vicinity of the reading part 3A. This is because the reflection light amount at the manuscript surface 3 of the secondary lighting light P3′ is changed based on the manuscript density. This flare phenomenon frequently occurs at a part where the manuscript density is drastically changed.
An example of this is explained below. That is, as roughly shown in FIG. 2-(a), the cylinder shaped lamp 4 is scanned in the sub scanning direction so as to be scanned on the manuscript surface 3 and the image of the manuscript surface 3 is read. The manuscript surface 3 has a black pattern part 8A, a black pattern part 8B, a white pattern part 8C between the black pattern part 8A and the black pattern part 8B, and a white pattern part 8D which is a remaining part.
In a case where the cylinder shaped lamp 4 is scanned in the sub scanning direction of the manuscript surface 3, turning attention to a designated point Q of the reading part 3A extending in a line shape, a diffusion reflection light from a remaining point Q′ of the reading part 3A extending in a line shape, and a part of a diffusion reflection light from a vicinity in front and behind in the sub scanning direction put between the reading part 3A extending in a line shape, return inside of the cylinder shaped lamp 4 through the irradiation opening part 4A and reflect at the inside part wall surface 4B, so as to become a secondary lighting light P3′ which lights again to the point Q of the reading part 3A. In a case where the manuscript density is uniform, for example, the cylinder shaped lamp 4 is scanning the white pattern part 8D, there is no change of the light amount of the secondary lighting light P3′. Hence, in a case where the manuscript image is read out, the image 8D′ becomes uniformly white as shown in FIG. 2-(b).
However, in a case where the black patterns 8A and 8B of the manuscript surface 3 are read out, turning attention to a point R of the white pattern part 8C corresponding to the point Q of the white pattern part 8D, due to the existence of the black patterns 8A and 8B, the light amount of the diffusion reflection light from a remaining point of the reading part 3A having a line form and the diffusion reflection light from front and behind vicinities in a sub direction put between the line shape reading part 3A is smaller than the light amount when the white pattern part 8D of the manuscript surface 3 is read.
Meanwhile, the secondary lighting light P3′ is diffusion reflected by the reading part 3A having a line form, returns inside of the cylinder shaped lamp 4 through the irradiation opening part 4A, reflects at the inside part wall surface 4B, and lights again a point R of the reading part 3A. Therefore, the light amount of the secondary lighting light P3′ is smaller than the light amount when the white pattern part 8D is read. Hence, the white pattern part image 8C′ between the black pattern part image 8A′ and the black pattern part image 8B′ is darker than the white pattern part image 8D′. The substantially same phenomenon is generated at the white pattern part 9′ in the vicinity of the interface area of the white pattern part 8D and the black patterns 8A and 8B in a sub scanning direction.
Therefore, in a design of the image reader apparatus, although the optical system part arranged inside of the housing is painted black and a layout of the respective optical system parts is devised, it is difficult to eliminate relighting at the reading part by the secondary lighting light. Hence, that causes difficulty for improvement of the quality of reading an image.
In the image reader apparatus shown in the above-mentioned laid opened patent application H09-130540, although the diffusion reflection light of the lighting light reflected at the reading part 3A is prevented from returning to the cylinder shaped lamp 4, it is not possible to prevent the generation of the flare phenomenon in the manuscript image by using the optical parts with a low price.